1. Field of the Invention
The present invention relates to a semiconductor device including a lead frame having a three-layer structure of an intermediate layer formed as a metal made etching stop layer, a lead formed of a thick metal layer on one surface of the intermediate layer, and a lead formed of a thin metal layer on the other surface thereof, wherein a bump formed of the intermediate layer is formed on the lead formed of the thin metal layer, whereby making the lead frame as an electrode leading means by directly connecting the bump to each electrode of a semiconductor element.
One type of semiconductors has a such structure as using a lead frame and connecting an electrode of the semiconductor device to the extreme end of the inner lead thereof through a gold wire.
Another type of a semiconductor has such a structure as using a TAB lead in place of the lead frame, which includes a polyimide film as a base and a lead made of a silver foil formed on the surface of the base, and directly connecting the inner lead of the TAB lead to the pad of the semiconductor element.
The other type of semiconductors has such a structure as using the lead frame with the inner lead on which a bump is formed, and connecting the bump to the electrode pad of the semiconductor element without any wire.
Incidentally, the semiconductor device using the lead frame and connecting the inner lead thereof to the electrode pad of the semiconductor element through a gold wire has the following disadvantage: namely, the tendency of thinning of the package is restricted due to deflection of the wire and the reduction in a cost is also restricted by the use of the gold wire; and it is difficult to make the disposed pitch of each inner lead less than 120 .mu.m and hence to satisfy the tendency of increasing pins.
Also, the semiconductor device using the TAB lead has a disadvantage that, since the outer lead is formed of the silver foil to the same thickness as that of the inner lead, it is difficult to obtain the necessary strength as the outer lead. Further, since it is difficult to thin the silver foil stuck on the polyimide base and hence to obtain the fine pitch.
Accordingly, in the viewpoints of the tendencies of thinning and fine pitching and of securing strength of the outer lead, there can be proposed the semiconductor device using the lead frame with the inner lead on which a bump is formed, and connecting the bump to the electrode pad of the semiconductor element without any wire. However, in the existing circumstance, there is not developed the concrete technique to secure the strength of the outer lead at a desired value while satisfying the tendency of fine pitching.